1. Field of the Invention
The present invention relates to an image stabilization control circuit for driving an image stabilization mechanism provided in order to compensate for camera shake or other types of vibration in an image-capturing device such as a digital still camera, and to an image-capturing device using the control circuit.
2. Description of the Related Art
Current image-capturing devices are often provided with a camera shake correction function in order to minimize a decline in picture quality due to camera shake. Many types of camera shake correction methods exist. In one of the methods, vibration of the image-capturing device is detected by a vibration detector, and an optical component such as a correction lens, or an image sensor such as a CCD image sensor, is displaced by an actuator on the basis of the detected signal. The vibration detector employs a gyro-sensor and detects angular velocity that corresponds to the change in the direction of the optical axis. The degree to which the lens or other component is displaced is used to drivably control the actuator. Therefore, the image stabilization control circuit for generating the drive signal of the actuator performs a process whereby the angular velocity or other type of displacement velocity obtained from the vibration detector is integrated and converted to the displacement magnitude.
More particularly, the process for obtaining the displacement magnitude involves performing a camera shake component extraction process to remove frequency components below the region of camera shake vibration frequencies from the angular velocity signal outputted from the gyro-sensor, and using integration to convert the angular velocity into a displacement magnitude corresponding to an angle. In the process for obtaining the displacement magnitude, by damping the output signal of the integration process or by other means, a centering process is also performed to establish the displacement magnitude so that it is made more difficult for the lens or the like to reach the movability limit. The processor for generating the output corresponding to the displacement magnitude on the basis of the output signal of the gyro-sensor is herein referred to as a gyro-filter.
The function of a gyro-filter is conventionally achieved using software for which a microprocessor is used. A problem presented with such a configuration is that more power is consumed when the frequency of the clock for driving the microprocessor is increased to make the image stabilization more responsive. Addressing this problem by using a digital filter circuit instead of a microprocessor as the gyro-filter makes it possible to decrease power consumption.
The gyro-sensor outputs an analog signal corresponding to the displacement velocity. The analog signal is converted to fixed-point format digital data by an analog-to-digital converter (ADC), and fed to the gyro-filter. The vibration compensation data outputted by the gyro-filter as a computational result is used to generate the drive signal of the actuator. The drive signal is generated using, for example, a digital-to-analog converter (DAC) or a pulse width modulation (PWM) circuit. A DAC or PWM circuit that receives fixed-point format data as an input is used for the sake of structural simplicity and other reasons. Specifically, the gyro-filter receives displacement velocity in a fixed-point format, and outputs vibration compensation data in a fixed-point format. For this reason, calculations within the gyro-filter can also be performed substantially in fixed-point format.